Among the conventionally-known walk-behind agricultural working machines are one (disclosed, for example, in Japanese Patent Laid-open Publication No. 2001-238504 (hereinafter “patent document 1”)) that includes, in its rear section, a guide arm for regulating the position of an auxiliary working device drawn by the agricultural working machine (hereinafter also called a “machine-drawn working device”), and one (disclosed, for example, in Japanese Patent Laid-open Publication No. HEI-10-225205 (hereinafter “patent document 2”)) that includes, in its rear section, an elevator mechanism for vertically moving any one of various machine-drawn working device connected to the elevator mechanism.
FIG. 19A is a side view showing principal components in a rear section of the conventional walk-behind agricultural working machine disclosed in the above-mentioned patent document 1 and auxiliary working device drawn by the working machine. Frame plate 202 is secured to a rear portion of a power transmission case 201 provided on the walk-behind agricultural working machine which is constructed as a tiller or cultivator, and a machine-drawn working device 204, which is constructed as a ridger or ridge forming device 204, is connected to a rear end portion of a drawing bar 203 pivotally connected to the frame plate 202 via a horizontal lower pivot shaft 202a. Guide arm 205 is vertically pivotably connected to the frame plate 202, and has an upward movement restricting portion 206 for regulating the position of a lower pin shaft 207 provided on the drawing bar 203. The guide arm 205 also has an upward/downward movement restricting portion 206a for regulating the position of an upper pin shaft 207 provided on the drawing bar 203. The drawing bar 203 has a holder 208 provided on its rear end portion for insertion therethrough a vertical stay 311, and it connects the ridger 204 to the working machine by fixing the stay 311 to the holder 208 by means of a locking member 312. Further, an operating angle of a middle blade 215 of the ridger 204 can be changed about a pivot point 314 by the human operator turning a knob 313, and a vertical position (height) of the tail wheel 217 can be changed by the human operator turning an adjusting handle 316.
FIG. 19B is a side view of the agricultural working machine disclosed in patent document 1. In the disclosed agricultural working machine 414, the ridger 204 can be shifted to a raised inoperative position as shown by causing the drawing bar 203 with the stay 311 to pivot upwardly about the lower shaft 202a and locking the drawing bar 203 and stay 311 in the raised position via the guide arm 205 of FIG. 19A. Reference numeral 315 in FIG. 19B represents an operating handle of the agricultural working machine 414.
FIG. 20 is another side view of the walk-behind agricultural working machine 414, which shows how it operates, i.e. how the working machine 414 forms hard earth 213 into cultivated soil 214 via cultivating claws 212 and forming ridges via the ridger 204 while traveling on wheels (only one of which is shown) 211.
In the illustrated example of FIG. 19A, when the pin shafts 207 are restricted in position by the movement restricting portions 206 and 206a formed on the guide arm 205, the traveling wheels 211 are prevented from moving downward relative to the ridger 204. Thus, prior to initiation of ridging operations when the lower surface of the ridger 204 contacts the soil, the driving traveling wheels 211 would float above the soil, so that no driving force can be obtained from the traveling wheels 211. If the human operator depresses the operating handle of the agricultural working machine 414 device to force the traveling wheels 211 into contact with the soil, then the necessary driving force can be obtained from the traveling wheels 211, and therefore desired operations can be carried out as illustrated in FIG. 20; however, in this case, loads on the operator would increase.
When the height of ridges to be formed by the ridger 204 is to be adjusted in the agricultural working machine of FIGS. 19A and 19B and 20, the vertical position of the ridger 204 can be changed, for example, by {circumflex over (1)} vertically moving the stay 311 relative to the holder 208 and then fixing the stay 311 by means of the locking member 312, {circumflex over (2)} turning the knob 313 to change the angle of the middle blade 215 of the ridger 204 and/or {circumflex over (3)} tuning the adjusting handle 316 to vertically move the tail wheel 217 of the ridger 204. However, these three approaches {circumflex over (1)}-{circumflex over (3)} can only adjust the vertical position of the ridger 204 with respect to the drawing bar 203; they can never adjust the vertical position of the ridger 204 with respect to the power transmission case 201, because the drawing bar 203 and ridger 204 pivot about the lower shaft 202a relative to the power transmission case 201.
Furthermore, because upward movement of the ridger 204 is restricted by cooperation between the movement restricting portions 206 and 206A and pin shafts 207 via the drawing bar 203, the ridger 204 is not allowed to move higher than a predetermined height with respect to the power transmission case 201. Namely, because the ridger 204 can freely pivot while it is below a predetermined height, it is difficult to form ridges with a uniform height.
In the agricultural working machine 414 shown in FIGS. 19A and 19B, the ridger 204 can be raised, via the drawing bar 203, stay 311, etc., to a higher inoperative position farther away from the soil, if the lengths of the drawing bar 203 and stay 311 are increased. Capability to raise the ridger 204 to a higher inoperative position like this is advantageous in that the ridger 204 is prevented from contacting the soil when the agricultural working machine 414 makes a turn during the course of the agricultural work or when the machine 414 just travels for a certain purpose other than the agricultural work. Further, the capability can prevent the ridger 204 from contacting the soil even when the traveling wheels of the agricultural working machine 414 have sunk down into soft soil. In addition, the capability can prevent the ridger 204 from interfering with steps of the human operator walking while manipulating the operating handle 315. However, the increased lengths of the drawing bar 203 and stay 311 would increase the overall weight of the agricultural working machine 414, thereby degrading the maneuverability and operability. Further, when the ridger 204 is lowered to its operative position for ridging, it gets very close to the legs and feet of the human operator, which results in degraded operability.
FIG. 21 is a side view of the walk-behind agricultural working machine 231 disclosed in the above-mentioned patent document 2, which particularly shows a seeding device 232 connected as a machine-drawn working device to a rear section of the working machine 231 via the elevator mechanism 242 so that the seeding device 232 can be vertically moved as desired. Reference numeral 234 represents a rotary device having rotary claws 235, and 236 one of traveling wheels attached to an axle 237.
FIG. 22 is a side view of the elevator mechanism 242 of the walk-behind agricultural working machine 231, which particularly shows that a speed change guide member 241 is attached to a rear portion of a power transmission case and the elevator mechanism 242 is attached to the speed change guide member 241. The elevator mechanism 242 includes a link support member 244 connected to the speed change guide member 241, upper and lower links 245 and 246 having respective one ends pivotably connected to the link support member 244, and a body-side hitch (i.e., connection section) 247 pivotably connected to the respective other ends of the upper and lower links 245 and 246. The seeding device 232 is secured to the body-side hitch 247. The upper link 245 has a slide pin 251 provided on its middle portion. Lower limit position of the body-side hitch 247 can be controlled by placing the slide pin 251 in engagement with a downward-movement restricting recess 252, while an upper limit position of the hitch 247 can be controlled by placing the slide pin 251 in engagement with an upward-movement restricting recess 253. Reference numeral 254 represents a pivot pin shaft pivotably supporting an end portion of the upper link 245 adjacent to the link support member 244, and 255 represents a coupling pivot shaft pivotably supporting an end portion of the lower link 246 adjacent to the link support member 244. Further, one-dot-dash lines in the figure are explanatory of a manner in which the lower limit position of the body-side hitch 247 is controlled by the downward-movement restricting recess 252, while solid lines are explanatory of a manner in which the upper limit position of the body-side hitch 247 is controlled by the upward-movement restricting recess 253.
When the seeding device 232 is lowered by the elevator mechanism 242 to a position for performing desired operations as illustrated in FIG. 21, the upper and lower links 245 and 246 slant rearwardly and downwardly as illustrated in FIG. 22. If the walk-behind agricultural working machine 231 is moved forward with the upper and lower links 245 and 246 slanting rearwardly and downwardly, a traction force T1 is produced in a forward and upward direction along the length of the upper and lower links 245 and 246 as illustrated in FIG. 22. Therefore, when the seeding device 232 is being drawn by the agricultural working machine 231, a vertically-upward component force T2 of the traction force T1 would make it difficult to keep the seeding device 232 at an appropriate vertical position.
For example, when the vertical position of the seeding device 232 is to be adjusted with the slide pin 251 engaging with the downward-movement restricting recess 252, the human operator vertically moves the operating handle to incline both of the agricultural working machine 231 and seeding device 232 in a forward or rearward direction, and thus loads on the human operator would increase. Furthermore, keeping the seeding device at a constant height would require considerable skills and experiences on the part of the human operator.
Further, as the upper and lower links 245 and 246 are caused to pivot upward in FIG. 22, the lower link 246 comes into abutment against the pivot pin shaft 254 supporting the upper link 245. Namely, because the upper and lower links 245 and 246 are coupled to the link support member 244 via the coupling pivot shaft 255, pivotable ranges of the upper and lower links 245 and 246 are considerably limited, which would limit the height of the seeding device 222 raised to its inoperative position (i.e., raised height of the seeding device 232).